diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
index a6ed9849e77..5748aa9a1a9 100644
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -2886,14 +2886,16 @@ MergeWithExistingConstraint(Relation rel, const char *ccname, Node *expr,
  * for each column, giving priority to user-specified ones, and setting
  * inhcount according to how many parents cause each column to get a
  * not-null constraint.  If a user-specified name clashes with another
- * user-specified name, an error is raised.
+ * user-specified name, an error is raised.  'existing_constraints'
+ * is a list of already defined constraint names, which should be avoided
+ * when generating further ones.
  *
  * Returns a list of AttrNumber for columns that need to have the attnotnull
  * flag set.
  */
 List *
 AddRelationNotNullConstraints(Relation rel, List *constraints,
-							  List *old_notnulls)
+							  List *old_notnulls, List *existing_constraints)
 {
 	List	   *givennames;
 	List	   *nnnames;
@@ -2905,7 +2907,7 @@ AddRelationNotNullConstraints(Relation rel, List *constraints,
 	 * because we must raise error for user-generated name conflicts, but for
 	 * system-generated name conflicts we just generate another.
 	 */
-	nnnames = NIL;
+	nnnames = list_copy(existing_constraints);	/* don't scribble on input */
 	givennames = NIL;
 
 	/*
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 2f5b7007ff9..df1ba112b35 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -781,6 +781,7 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 	List	   *rawDefaults;
 	List	   *cookedDefaults;
 	List	   *nncols;
+	List	   *connames = NIL;
 	Datum		reloptions;
 	ListCell   *listptr;
 	AttrNumber	attnum;
@@ -1335,11 +1336,20 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 	/*
 	 * Now add any newly specified CHECK constraints to the new relation. Same
 	 * as for defaults above, but these need to come after partitioning is set
-	 * up.
+	 * up.  We save the constraint names that were used, to avoid dupes below.
 	 */
 	if (stmt->constraints)
-		AddRelationNewConstraints(rel, NIL, stmt->constraints,
-								  true, true, false, queryString);
+	{
+		List	   *conlist;
+
+		conlist = AddRelationNewConstraints(rel, NIL, stmt->constraints,
+											true, true, false, queryString);
+		foreach_ptr(CookedConstraint, cons, conlist)
+		{
+			if (cons->name != NULL)
+				connames = lappend(connames, cons->name);
+		}
+	}
 
 	/*
 	 * Finally, merge the not-null constraints that are declared directly with
@@ -1348,7 +1358,7 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 	 * columns that don't yet have it.
 	 */
 	nncols = AddRelationNotNullConstraints(rel, stmt->nnconstraints,
-										   old_notnulls);
+										   old_notnulls, connames);
 	foreach_int(attrnum, nncols)
 		set_attnotnull(NULL, rel, attrnum, true, false);
 
diff --git a/src/include/catalog/heap.h b/src/include/catalog/heap.h
index 624c415dadb..6c9ac812aa0 100644
--- a/src/include/catalog/heap.h
+++ b/src/include/catalog/heap.h
@@ -117,7 +117,8 @@ extern List *AddRelationNewConstraints(Relation rel,
 									   const char *queryString);
 extern List *AddRelationNotNullConstraints(Relation rel,
 										   List *constraints,
-										   List *old_notnulls);
+										   List *old_notnulls,
+										   List *existing_constraints);
 
 extern void RelationClearMissing(Relation rel);
 
diff --git a/src/test/regress/expected/create_table.out b/src/test/regress/expected/create_table.out
index 029beb20aae..90639ea0d89 100644
--- a/src/test/regress/expected/create_table.out
+++ b/src/test/regress/expected/create_table.out
@@ -161,6 +161,12 @@ ALTER TABLE remember_node_subid ALTER c TYPE bigint;
 SAVEPOINT q; DROP TABLE remember_node_subid; ROLLBACK TO q;
 COMMIT;
 DROP TABLE remember_node_subid;
+-- generated NOT NULL constraint names must not collide with explicitly named constraints
+CREATE TABLE two_not_null_constraints (
+   col integer NOT NULL,
+   CONSTRAINT two_not_null_constraints_col_not_null CHECK (col IS NOT NULL)
+);
+DROP TABLE two_not_null_constraints;
 --
 -- Partitioned tables
 --
diff --git a/src/test/regress/sql/create_table.sql b/src/test/regress/sql/create_table.sql
index 9b3e93b4164..80e424e6bda 100644
--- a/src/test/regress/sql/create_table.sql
+++ b/src/test/regress/sql/create_table.sql
@@ -105,6 +105,13 @@ SAVEPOINT q; DROP TABLE remember_node_subid; ROLLBACK TO q;
 COMMIT;
 DROP TABLE remember_node_subid;
 
+-- generated NOT NULL constraint names must not collide with explicitly named constraints
+CREATE TABLE two_not_null_constraints (
+   col integer NOT NULL,
+   CONSTRAINT two_not_null_constraints_col_not_null CHECK (col IS NOT NULL)
+);
+DROP TABLE two_not_null_constraints;
+
 --
 -- Partitioned tables
 --